Inflatable packers typically comprise a flexible element mounted on a mandrel with one stationary collar and one movable collar at an opposite end. Typically a system of valves is used to get pressurized fluid into the annular space between the mandrel and the element to start the inflation process. The inflation allows the element to expand radially into sealing contact with a surrounding tubular or wellbore, made possible by the movable collar riding up toward the stationary collar, which is usually located near the uphole end. The valve system includes a check valve to hold the applied pressure in the annular space between the mandrel and the element. Other types of inflatables known as External Casing Packers use fixed collars and reinforcement only on the ends of the element.
In the earlier designs, the inflation medium was drilling mud or other liquids. Inflating the element with such liquids had certain drawbacks. One problem was thermal effects that could cause a pressure reduction under the inflated element and a loss of seal. Another drawback was that damage to the element either from installation or during service in the well over a period of time could result in a tear or rupture of the element and a loss of seal as the fluid escaped, either slowly or virtually immediately depending on the nature of the failure in the element. While the valve system had provisions for avoiding overpressure, the risks to the integrity of the element were real and present and resulted in failures.
In an effort to improve inflatable performance, cement slurry was used as the inflation medium. The idea was that the slurry, in a pumpable condition, would be delivered into the annular space between the mandrel and the element and under pressure. The slurry would then set up with the hope that, once set up, the slurry, now in solid form would help to hold the seal of the packer even if the element experienced a failure. However introducing cement slurry created several new problems. First, there were added risks of getting the slurry through the various valves of the inlet assembly without fouling their operation. Second, the use of cement slurry required specialized equipment at the surface. Some applications, particularly offshore, created logistical problems in locating such equipment on platforms and created increased expense due to the logistical issues. Furthermore, when using cement slurry, time was of the essence in spotting and pumping the slurry behind the element. It was also important to quickly remove any excess slurry to avoid having to drill it out if it impeded later operations. As if all these issues were not enough of a concern, there was yet another downside to the use of the cement slurry. The slurry, upon setting, actually reduced in volume. This made the packer more likely to lose its sealing contact after it was set.
The prior art fluid inflatable packers are described in U.S. Pat. Nos. 4,897,139; 4,967,846 and 5,271,469. Cement inflatable packers are described in U.S. Pat. No. 5,738,171.
The present invention addresses the shortcomings of the past systems for inflation of the element and retention of the seal after inflation. The element is inflated with a fluid, as before. However, a layer is inserted in the annular space between the element and the mandrel that, upon contact with the inflating fluid absorbs the inflating fluid and expands so that the expanded volume of the fluid and the expanding layer is preferably as great as the volume of the two layers prior to absorption. The resulting advantage is retention of the seal despite a failure in the element as the expanding layer with the retained fluid provides the continuing sealing force. Furthermore, there is no volume loss after inflation as occurred in the prior design using cement slurry that could undermine the sealing force of the inflated element. Those and other advantages of the present invention will become more readily apparent to those skilled in the art from the description of the preferred embodiment, the drawings and the claims that appear below.